Novel thiols and disulphides

ABSTRACT

The invention provides a process for preparing a thiol of formula I or a disulphide of formula II   wherein R is aryl which may be substituted by alkyl, aralkyl or an electron releasing substituent, and R1 is hydrogen, alkyl or aryl which may be substituted by alkyl, aralkyl or an electron releasing substituent, or R and R1 taken together represent an alkylene chain of from 4 to 7 carbon atoms which may be substituted by alkyl, aralkyl, or aryl, which process comprises treating an Alpha -amino nitrile of formula III   wherein R and R1 are as defined above and R2 is alkyl or aralkyl, with hydrogen sulphide and if desired oxidising a thiol of formula I to a disulphide of formula II.

United States Patent [1 1 Curran et al.

[451 Sept. 23, 1975 NOVEL THIOLS AND DISULPHIDES [75] Inventors: Adrian Charles Ward Curran;

Roger Crossley, both of Reading, England [73] Assignee: John Wyeth & Brother Limited,

Maidenhead, England 22 Filed: Mar. 18,1974

21 Appl. No.: 452,029

[30] Foreign Application Priority Data Mar. 29, 1973 United Kingdom 15066/73 [52] U.S. Cl. 260/609 D; 260/608; 260/551 S;

260/465 E [51] Int. Cl? C07C 149/00 [58] Field of Search 260/608, 609 R, 609 D Primary ExaminerLewis Gotts Assistant ExaminerD. R. Phillips ABSTRACT The invention provides a process for preparing a thiol of formula 1 or a disulphide of formula II RCHSH Rci-isseHR R R, n

wherein R is aryl which may be substituted by alkyl, aralkyl or an electron releasing substituent, and R is hydrogen, alkyl or aryl which may be substituted by alkyl, aralkyl or an electron releasing substituent, or R and R taken together represent an alkylene chain of from 4 to 7 carbon atoms which may be substituted by alkyl, aralkyl, or aryl, which process comprises treating an a-amino nitrile of formula III wherein R and R are as defined above and R is alkyl or aralkyl, with hydrogen sulphide and if desired oxidising a thiol of formula I to a disulphide of formula II.

6 Claims, No Drawings NOVEL THIOLS AND DISULPHTDES The invention relates to a new process for the preparation of thiols and disulphides and to'sorne novel thiols and disulphides'obtained thereby.

Thioamides are commonly prepared by reaction of nitriles with hydrogen sulphide usually in the presence of pyridine and triethylaminei.Although-'the'reaction between a-amino nitriles and hydrogensulphide has been little investigated such reactions? that have been reported have-generallygiven thioamides as products. l

We" have now surprisingly found that thiols and disulphides can'be prepared,.often in high yields, by reacting certain a-amino nitriles with hydrogen sulphide, This result is surprising since one would expect on the basis of the general literature tha'tthe products would be thioamides.=-

r r 7 Accordingly the present invention provides a process for preparingfathiol of formula I or 'a'disulphide of forwherein R and R, areas defined above and R is alkyl or aralkyl, with hydrogen sulphide, preferably in the presence of a base, and if desired or necessary oxidising a thiol of formula 1 to'a disulp'hide' of formula H.

The reaction with hydrogemsulphide preferably carried out in the ,presenceofsabase, e.g.f-a tertiary amine suchas a trialkylaniine preferably triethylamine.

A solvent e.g.,aweakly basic solventsuch as pyridine or lutidinesmay be us ed- Examples of aryl groups used in phs yl a fiaphthy rw ln nlaryl g oup ca one or more electron releasing spbstituents such substituentsinclude hydroxy,;h alog'en, e,g, chlorine, bromine, fluorine orjodine,alkbxy,e.g. lower alkoxy such as methoxy, ethoxy, and propoxy,.amino, substituted amino including 'mono and di-alkylamino and mono and di-ara lkylf'amino e.g. diniethylaniino and dibe n zylami'no, and 'di substituted aminoi'n'which'the'jsub pyrrolidino. When an aryl group is phe'riyl it may be" mono-substituted e.g. at the 4-position, disubs'tit'ute'd,

e.g. at the 3 and 1 positions, or trisub'sti 'tut'eiiiefgl at the 3,4 and 5 positions.

Alkyl groups used as groups R, R, and R, in the 'stituentsare joined together to form a ringwith thenif" :trogen' of the arriino', e.g. piperidinmgmorph ,ljn'oand b,

above formulae, or'as substituents on other groups, include n-, sand t-lower alkyl groups e.g. methyl, ethyl, n-, sandt-butyl and cycloalkyl groups e.g. cyclobutyl,

They have (MeO)=C l-l CHSl-l is an intermediate for the corre sponding disulphide, diveratryldisulphide,whichis it self a flavouring agent for foods and beverages (U.S.

2 cyclopentyl and cyclohexyl. Aralkylgrou'ps include aryllower alkyl such as berizyL-phenethyl and phenpropy Oftenthe process 'of the invention givesthethiol or disulphide in high yield but sometimes a thioamide may be formed as a by-product; In general when R is aryl substituted by an e'le'ctron rele'asing group formation of the thiol of disulphide'predomina'tes and when R is also a branched chain alkyl or aralkyl group with a secondary or tertiary carbon atom attached directly to the nitrogen no significant amount of thioamide byproduct appears to be formed.

The product of the process of the invention is initially a thiol butsince thiols are readily oxidised to disulphides the thiols may oxidise in air to give the corren sponding disulphides. This oxidation can be avoided by conducting the reaction in the absence, of air e.g. under nitrogen. Where a disulphide is desired this can be formedby oxidation of the thiol e.g. by allowing the reaction mixture to stand or by bubbling air, or oxygen through the mixture. Generally standard oxidation con.- ditionsforthis reaction may be used see Kharasch, Or-

ganic Sulphur Compounds, Pergamon Press Oxford The disulphides may be reduced back to the thiols by standard means e.g. by sodium sulphide which gives the thiol as the sodium salt.

The thiols and disulphides prepared in this invention are either known compounds or are novel compounds. various uses. ,For instance 3,4

Pat. No. 2,957,9l9). Generallyt'he thiols find application as corrosioninhibitorsand reducing agents, e.g.,in

photographic compositions. The novel compounds are those" of, formula I or" wherein R is phenyl substituted by a single alkoxy group and R, is hydrogen and are included in the invention.

are either known compounds or novel compounds which can be prepared from known intermediates as illustrated in the Examples below, The following examples illustrate the invention, temperatures'being in C. EXAMPLE) L, i V

'3,4-Dimethoxybenzylmercaptan ll sopro pylami no-dz-i3,4 dimethoxyplie nyl)acetonitrile preparedfrom' veratr aldehyde according to the methodof G. Morris (J.O.C. l96l, 26, 474l) and isolatedin 79% .yield as colourless needles from isopr'opylet her' m.p. 102.

The aminonitrile (5 gm) was dissolved in a mixture of pyridine 2Q ml.) and triethylamine (6 ml) and the solution treated with hydrogen sulphide at room temperature for 2 hours with stirring. The red solution wasv transferred to a sealed flask and allowed to stand at room temperature for 16 hours. Removal of the volatile material in vacuo, gave a residual brown oil which was dissolved in ether (lOO ml) and washed with water (3 X 15 ml), 2T3, HCl(2 X 50 ml) and-water (2 X 50 ml). The ethereal solution was, dried. and evaporated in vacuo to give the title compound as a pale yellow oil (3.7 'gm., 92%).[GLC Rf=5% min |0% X E 60,

'T=200; I=240)]. The acid*extract -were combined and'the pH adjusted to -l2.'0 with 2N NaOl-l. and extractedinto ether ('3 X 50 ml.).'The combined ethereal Thea-amino nitrile starting materials offorrntila lll extracts were washed with brine (2 X 50 ml.), dried and evaporated in vacuo to give no product (i.e. no starting material or aminothioamide).

The title compound was fully characterised by converting to the 2,4-dinitrophenyl ether as described by Vogel( Practical Organic Chemistry p.485). 3,4- Dimethoxybenzyl (2,4-dinitrophenyl)sulphide was isolated as yellow needles (95% yield) m.p. 159 [Foundz C,5l.75; H.413; N,7.87% c,,H,.N,0,s requires: C,5l.42; H,4.03; N,7.99%].

EXAMPLE 2 4-Methoxybenzyl disulphide.

a-lsopropylamino-a-(4-methoxyphenyl)acetonitrile was prepared according to the method of G. Morris et a1. (J.O.C. 1961, 26, 4741) and isolated in 73% yield as a colourless oil which was further characterised as the hydrochloride, prepared by passing dry HCl gas into an ethereal solution, isolated as colourless needles m.pt. 123 (dec). [Foundz C,60.0l; H,7.30; N,] 1.31% C H N O requires: C,59.87; l-l,7.12; N,11.64%].

The title compound was prepared from a-isopropylamino-a-(4-methoxyphenyl)acetonitrile, by the method described in Example I, and was isolated in 85% yield as colourless needles m.p. 101.6. (Found: C,63.02; l-l,5.94% C I-1 8,0 requires: C,62.7l; H,5.92%).

EXAMPLE 3 3,4-Dimethoxybenzylmercaptan a-tert. Butylamino-a-(3,4-dimethoxyphenyl)acetonitrile was prepared according to the method of G. Morris (loc.cit.) and was isolated in 80% yield from isopropanol as colourless needles m.p. 69.5".

The title compound was prepared from a-tert. butylamino-a-( 3 ,4-dimethoxyphenyl )acetonitrile according to the method described in Example 1 and was isolated as a pale yellow oil *80% yield) which was identical by G.L.C. comparison (10% XE 60, T=200, 11-240" RF=% min) and infra-red comparison with the 3,4- dimethoxybenzyl mercaptan isolated in Example 1.

EXAMPLE 4 a-Methylbenzylmercaptan.

a-lsopropylamino-a-phenylpropionitrile was prepared from acetophenone according to the method described in Org. Syn. Coll. Vol. IV, p.58. and was isolated as a colourless oil (96% yield) which was converted to the hydrochloride in the usual way (see Example 2) and was isolated as colourless needles m.p. 109 (isopropanol-ether). [Foundz C,64.08; l-l,7.61; N,l2.21% c,,H,,N,.r-ic1 requires C,64.l4; H,7.62; N,l2.46%].

The title compound was prepared from a-isopropylamino-a-phenylpropionitrile by the general method described in Example I, and was isolated as a colourless oil (96% yield) and characterised as the mercuric chloride derivative m.pt. 72- [Found: Cl,8.39; S,9.53. HgCl(C l-l,S) requires: Cl,9.50; S,8.59%] (Lit. m.p. 735 Ref. Beilstein Band 529 Ill, 1967.).

EXAMPLE 5 Cyclohexylmercaptan a-lsopropylaminocyclohexanecarbonitrile was prepared from cyclohexanone according to the method of G. Morris (J.O.C. 1961, 26, 4741) and was isolated as a colourless oil (95% yield) which was fully characterised as the hydrochloride prepared in the usual way and isolated as colourless needles m.p. 132 (dec. lFound: C,59.38; H,9.68; N,l3.79%.v C H N,.HCl requires: C,59.25; H,9.45; N,13.82%].

Treatment of a-isopropylaminocyclohexanecarbonitrile with H 5 under the conditions described in Example I gave the title compound as a colourless oil (8% yield) with recovery of starting material from the acidbase extraction. a

Reaction with H,S for 7 hours and standing at RT. for 3 days gave 34% yield of thio1+ 60% starting material. Cyclohexylmercaptan was characterised as the 2,4: dinitrophenylthioether m.p. 148 (Vogel: Practical Org. Chem. p.486. m.p. 148).

EXAMPLE 6 3 ,4-Dimethoxybenzyldisulphide.

pz-Methylamino-a-(3,4-dirnethoxybenzyl)acetonitrile was prepared from veratraldehyde according to the method of J. Klosa (J.Prakt. Chem., 1961, 12, 258-63) and converted to the hydrochloride in the usual way (see Example 2) (65% yield) m.p. 152-4 (lit. 1534) [Foundz C,54.l9; H,6.22; .N,l1.04%. C I-1 N 0 HCl requires: C,54.44; H,6.23; N,ll.54%].

The title compound was prepared from a-methylamino-a-(3,4-dimethoxybenzyl)acetonitrile according to the general method described in Example I and isolated as a pale yellow solid yield) which recrystallised.- from isopropanol as colourless needles m.p. 83[Found: C,59.28; ll,6.14%. C H S, requiresz: C,59.99; l-l,6.05%].

In addition, the acid-base extraction procedure described in Example 1 gave a-methylamino-a-(3,4- dimethoxybenzyl)thioacetamide (20% yield) which was isolated as a pale yellow solid and recrystallised from ethanol as creamy needles m.p. 204 (dec.) [Found: C,55.27; 11.6.68; N,l 1.64%. C H N,SO; requires: C,54.98; H,6.71; N,1 1.66%].

EXAMPLE 7 Benzylmercaptan a-lsopropylamino-a-phenylacetonitrile was prepared from benzaldehyde according to the method of G. Mor-' ris (J.O.C. 1961, 26, 4741) and was treated with H,S as described in Example I to give the title compound as a colourless oil (56%) characterised as the 2,4- dinitrophenyl derivative m.p. (vogel Practical Org.Chem. m.p. 130). The title compound was oxidised in air to benzyldisulphide m.p. 7l.3 [Found: v C,68.74; l-l,5.92%. C I-I S, requires: (1,6 8.25; H,5.73%] (lit mpt.71, Heilbron, Dictionary of Org- .Compounds p.904 Hinsberg, Ber. 1912, 45, 2339). In addition, the acid-base extraction work up procedure gave a-isopropylamino-a-phenylthioacetamide as I colourless needles (36% yield) m.p. 98.6 [Foundz C,63. 92; H,7.93; N,13.4%. C H N,S requires: C,63.39; H,7.74; N,l3.48%].

We claim:

1. A process for preparing a thiol of formula R-lZHSH l (IN R-(\I-NHR,

wherein R and R are as defined above and R, is lower alkyl, with hydrogen sulphide in the presence of a pyridine solvent and a lower trialkylamine base and thereafter recovering the product.

2. A process as claimed in claim 1, wherein the base is triethylamine.

3. A process as claimed in claim 1 when carried out in a solvent selected from pyridine and lutidine.

4. A process as claimed in claim 1, wherein a compound is used in which R is lower alkoxy phenyl or dilower alkoxyphenyl and in which R is a branched chain lower alkyl group with a secondary or tertiary carbon atom attached directly to the nitrogen atom of the amino group.

5. A process as claimed in claim 4, in which R is isopropyl or t-butyl.

6. A process as claimed in claim 4, in which R is monoor di-methoxy phenyl. 

1. A PROCESS FOR PREPARING A THIOL OF FORMULA
 2. A process as claimed in claim 1, wherein the base is triethylamine.
 3. A process as claimed in claim 1 when carried out in a solvent selected from pyridine and lutidine.
 4. A process as claimed in claim 1, wherein a compound is used in which R is lower alkoxy phenyl or dilower alkoxyphenyl and in which R2 is a branched chain lower alkyl group with a secondary or tertiary carbon atom attached directly to the nitrogen atom of the amino group.
 5. A process as claimed in claim 4, in which R2 is isopropyl or t-butyl.
 6. A process as claimed in claim 4, in which R is mono- or di-methoxy phenyl. 